1. Interdisciplinary Center for Scientific Computing (IWR), University of Heidelberg, Im Neuenheimer, Feld 205, 69120 Heidelberg, Germany
2. Department of Computer Science, Electrical Engineering and Mathematical Sciences, Western Norway University of Applied Sciences, Inndalsveien 28, Bergen 5063, Norway
3. Department of Mathematics and Computer Science, University of Dschang, P. O. Box 67, Dschang, Cameroon